JP7465072B2 - Water-based ink for plate printing - Google Patents

Description

The present invention relates to a water-based ink for plate printing and a method of plate printing using the water-based ink.

2. Description of the Related Art Gravure printing, flexographic printing, letterpress printing, and the like, which use printing plates such as intaglio, lithographic, and letterpress plates, are widely used because they allow the quality of printing to be controlled by changing the form of the plate and enable high-definition printing.
Conventionally, oil-based inks have been widely used in plate printing such as gravure printing, but there are issues from the viewpoints of the working environment, global environment, disaster prevention, and also issues of residual solvents when used for food-related products, etc. In addition, since gravure printing requires a large amount of oil-based ink to be used, there is a problem that it is difficult to meet the market needs for high-mix, small-lot production.
For this reason, plate printing using water-based inks has been attracting attention, but water-based inks have problems such as poor ink transfer due to poor drying and poor wetting of the ink onto the plate surface due to surface tension, making it difficult to obtain high-quality printed matter.
In addition, with the development of the packaging industry, the use of flexible packaging materials as printing media is increasing. As flexible packaging materials, resin films such as polyethylene terephthalate (PET) and polypropylene (PP) are mainly used, but scratches or peeling of the printed image on the packaging reduces the value of the packaged product, so high adhesion of the printed image to a substrate such as a film (hereinafter also referred to as "substrate adhesion") is required in plate printing.

Patent Document 1 discloses an aqueous printing ink composition for gravure printing that has good printability such as leveling and trapping properties on non-permeable plastic film substrates, and contains a polyurethane resin, an acetylene glycol compound, and 10% by weight or less of propylene glycol ether. In the examples, carbon black, polyurethane resin, n-propyl alcohol, and water are mixed and kneaded, and then a polyurethane resin solution, water, propylene glycol monomethyl ether, etc. are mixed to prepare a black printing ink, and the viscosity is further adjusted with a mixed solvent to prepare a diluted ink. It also discloses that the polyurethane resin is obtained by neutralizing a solvent-based polyurethane resin solution with ammonia water to make it water-soluble, and then evaporating the solvent.

Patent Document 2 discloses an aqueous gravure ink that is environmentally friendly and capable of high-resolution printing, which contains a pigment, a polymer, a water-soluble organic solvent, a surfactant, and water, and the boiling point of the water-soluble organic solvent is 100 to 260°C, and the ink contains 10 to 35% by mass of the water-soluble organic solvent and 50 to 70% by mass of water. In the examples, the ink is prepared by neutralizing crosslinked polymer particles containing a pigment with sodium hydroxide, and further blending water-insoluble polymer particles with diethylene glycol monoisobutyl ether and the like. The crosslinked polymer particles containing a pigment are described as being obtained by adding water, sodium hydroxide, and an aqueous ammonia solution to a methyl ethyl ketone (MEK) solution of a water-insoluble polymer, adding carbon black and dispersing the mixture, distilling off the MEK, and further crosslinking with trimethylolpropane polyglycidyl ether.

JP 2016-44282 A International Publication No. 2017/47267

Conventional water-based inks for plate printing as described in Patent Documents 1 and 2 and the like are required to be further improved in terms of the transferability of the ink to low-liquid-absorbent printing media and the adhesion to the substrate.
The present invention relates to a water-based ink for plate printing that has excellent ink transferability and substrate adhesion even to low-liquid-absorbent printing media, and a plate printing method using said water-based ink.

The present inventors have found that the above-mentioned problems can be solved by using, in an aqueous ink, crosslinked water-insoluble polymer particles containing a pigment as a coloring material, water-insoluble polymer particles containing no pigment as a fixing agent, an organic amine compound as a polymer neutralizing agent, and the ink containing 1% by mass or more and 30% by mass or less of a water-soluble organic solvent having a specific boiling point.
That is, the present invention relates to the following [1] and [2].
[1] A water-based ink for plate printing, comprising: crosslinked water-insoluble polymer particles A containing a pigment; water-insoluble polymer particles B not containing a pigment; an organic amine compound; 1% by mass or more and 30% by mass or less of a water-soluble organic solvent having a boiling point of 100° C. or more and 260° C. or less; and water.
[2] A plate printing method, comprising printing on a low liquid-absorbent printing medium using the water-based ink described in [1] above.

The present invention provides a water-based ink for plate printing that has excellent ink transferability and substrate adhesion even for low-absorbency printing media, and a plate printing method that uses the water-based ink.

[Water-based ink for plate printing]
The aqueous ink for plate printing of the present invention (hereinafter also referred to as simply "ink") contains pigment-containing crosslinked water-insoluble polymer particles A (hereinafter also referred to as "pigment-containing crosslinked polymer particles A"), pigment-free water-insoluble polymer particles B (hereinafter also referred to as "polymer particles B"), an organic amine compound, 1% by mass to 30% by mass of a water-soluble organic solvent having a boiling point of 100° C. or more and 260° C. or less, and water.

The term "aqueous" means that water accounts for the majority of the medium.
"Low liquid absorption" is a concept including low liquid absorption and non-absorption of water-based ink. Low liquid absorption can be evaluated by the water absorption of pure water. More specifically, it means that the amount of water absorption per surface area of the printing medium when the printing medium is in contact with pure water for 100 ms is 0 g/ ^m2 or more and 10 g/ ^m2 or less. The amount of water absorption can be measured using an automatic scanning liquid absorption meter.
"Printing" is a concept that includes printing to record characters and images, and printing.
The meaning of "water-insoluble" will be described in the section on polymers below.

The water-based ink for plate printing of the present invention has excellent ink transferability and substrate adhesion even to low-liquid-absorbent printing media. The reason for this is not clear, but is thought to be as follows.
In the present invention, the pigment is contained in the water-based ink in the form of crosslinked water-insoluble polymer particles A containing the pigment, and the polymer is crosslinked with a crosslinking agent, so that the polymer is firmly adsorbed or fixed on the surface of the pigment.
The ink of the present invention contains 1% by mass or more and 30% by mass or less of a water-soluble organic solvent having a boiling point of 100° C. or more and 260° C. or less, which is thought to suppress drying of the ink and improve transferability to a printing medium, and because the pigment-containing crosslinked polymer particles A are crosslinked, swelling of the polymer is suppressed even when water on the printing plate evaporates, and further, charge repulsion by the organic amine compound maintains the ink at a low viscosity, so that a higher ink transfer rate can be maintained and transferability is improved.
The pigment-containing crosslinked polymer particles A have excellent dispersion stability in the ink, and when printed, they spread sufficiently on the low-liquid-absorbent print medium together with the pigment-free polymer particles B to cover the surface of the print medium, but part or all of the organic amine compound volatilizes from the print medium after printing. The volatilization of the organic amine compound makes the surfaces of the polymer particles A and B hydrophobic, increasing their affinity with the hydrophobic surface of the low-liquid-absorbent print medium, which is thought to improve adhesion between the printed image and the print medium.
It is also believed that the dispersion of the pigment-containing crosslinked polymer particles A in water on the printing medium is suppressed, and the aggregation of the particles A is promoted to form a strong coating, improving the adhesion between the printed image and the printing medium. Furthermore, it is believed that the water-soluble organic solvent in the ink contributes to the wettability of the ink to the low-absorbency printing medium.
It is believed that due to the synergistic effect of these factors, the water-based ink for plate printing of the present invention exhibits excellent transferability and excellent adhesion to the substrate after transfer.

<Pigment-containing crosslinked water-insoluble polymer particles A>
The pigment used in the present invention is contained in the ink as pigment-containing crosslinked water-insoluble polymer particles A (pigment-containing crosslinked polymer particles A).
The pigment-containing crosslinked polymer particles A are formed by crosslinking pigment-containing polymer particles A1 (hereinafter also referred to as "pigment-containing polymer particles A1"), and the pigment-containing crosslinked polymer particles A can be obtained by obtaining an aqueous dispersion of the pigment-containing polymer particles A1 and then crosslinking the polymer dispersing the pigment in the aqueous dispersion with a crosslinking agent.
The crosslinking agent may be a compound having two or more functional groups capable of reacting with the functional groups of the pigment-containing polymer particles A1.

(Pigment)
The pigment used in the present invention may be either an inorganic pigment or an organic pigment.
Examples of inorganic pigments include carbon black and metal oxides, and carbon black is preferred for black inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black. Examples of white inks include titanium dioxide, zinc oxide, silica, alumina, magnesium oxide, and other metal oxides. These inorganic pigments may be surface-treated with a known hydrophobic treatment agent such as a titanium coupling agent, a silane coupling agent, or a metal salt of a higher fatty acid.
Examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments.

The hue is not particularly limited, and in the case of chromatic inks, any chromatic pigment such as yellow, magenta, cyan, red, blue, orange, green, etc. can be used.
Specific examples of preferred organic pigments include one or more selected from C.I. Pigment Yellow 13, 17, 74, 83, 93, 97, 109, 110, 120, 128, 139, 151, 154, 155, 174, 180; C.I. Pigment Red 48, 57:1, 122, 146, 150, 176, 184, 185, 188, 202, 254; C.I. Pigment Orange; C.I. Pigment Violet 19, 23; C.I. Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 16, 60; C.I. Pigment Green 7, 36, and the like.
The above pigments may be used alone or in combination of two or more kinds.

<Polymer a1 constituting pigment-containing polymer particles A1>
The polymer a1 (hereinafter also referred to as "polymer a1") constituting the pigment-containing polymer particle A1 is not particularly limited as long as it has at least pigment dispersibility. The polymer a1 constituting the pigment-containing polymer particle A1 is crosslinked with a crosslinking agent to become a water-insoluble crosslinked polymer a2 (hereinafter also referred to as "polymer a2"). The polymer a1 before crosslinking may be either a water-soluble polymer or a water-insoluble polymer, but becomes a water-insoluble polymer by crosslinking.
In the present invention, the "water-insoluble" of polymer a1 means that when the polymer is dried at 105°C for 2 hours and reaches a constant weight, and dissolved in 100 g of water at 25°C, the amount of dissolution is 10 g or less, and the amount of dissolution of polymer a1 is preferably 5 g or less, more preferably 1 g or less. When polymer a1 is an anionic polymer, the amount of dissolution is the amount of dissolution when the anionic group of the polymer is 100% neutralized with sodium hydroxide. When polymer a1 is a cationic polymer, the amount of dissolution is the amount of dissolution when the cationic group of the polymer is 100% neutralized with hydrochloric acid.
The polymer a1 before crosslinking becomes the polymer a2 after crosslinking. From the viewpoint of the dispersion stability of the pigment, the polymer a2 is preferably present in the ink in a state in which the polymer a2 contains the pigment and is encapsulated therein.

From the viewpoint of improving the dispersion stability and storage stability of the pigment, the polymer a1 preferably has an ionic group. The ionic group is preferably an acid group, and more preferably a group that exhibits acidity by dissociating and releasing a hydrogen ion, such as a carboxy group (-COOM), a sulfonic acid group (-SO ₃ M), or a phosphate group (-OPO ₃ M ₂ ), or an acid group such as a dissociated ion form thereof (-COO ^- , -SO ₃ ^- , -OPO ₃ ^2- , -OPO ₃ ^- M). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. Of these, a carboxy group (-COOM) is preferable from the viewpoint of improving the dispersion stability and storage stability of the pigment.

The ionic group contained in the molecule of polymer a1 is preferably one that is introduced into the polymer skeleton by ionic monomer (a-1). That is, polymer a1 preferably contains a structural unit derived from ionic monomer (a-1). Examples of polymer a1 include vinyl resins, polyester resins, polyurethane resins, etc. Among these, vinyl resins are preferred.
The polymer a1 is more preferably a vinyl resin obtained by copolymerizing a raw material monomer (a) (hereinafter also simply referred to as "raw material monomer (a)") containing an ionic monomer (a-1) (hereinafter also referred to as "component (a-1)") and a hydrophobic monomer (a-2) (hereinafter also referred to as "component (a-2)").
The vinyl resin preferably contains a structural unit derived from the component (a-1) and a structural unit derived from the component (a-2). The vinyl resin may further contain a structural unit derived from a nonionic monomer (a-3) (hereinafter, also referred to as "component (a-3)").

[Ionic Monomer (a-1)]
The ionic monomer (a-1) is preferably an anionic monomer, such as a carboxylic acid monomer, a sulfonic acid monomer, etc. Of these, the carboxylic acid monomer is more preferred.
The carboxylic acid monomer may be at least one selected from (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid and 2-methacryloyloxymethylsuccinic acid, with (meth)acrylic acid being preferred.
In this specification, "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid, and "(meth)acrylate" means at least one selected from acrylate and methacrylate.

[Hydrophobic Monomer (a-2)]
In the present invention, the term "hydrophobic" with respect to the hydrophobic monomer (a-2) means that the dissolution amount is less than 10 g when the monomer is dissolved to saturation in 100 g of ion-exchanged water at 25° C. The dissolution amount of the hydrophobic monomer (a-2) is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of adhesion of the pigment to the substrate.

Examples of the hydrophobic monomer (a-2) include alkyl (meth)acrylates, aromatic group-containing monomers, and macromonomers having a polymerizable functional group at one end.
The alkyl (meth)acrylate is preferably one having an alkyl group having 6 to 18 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, (iso)propyl (meth)acrylate, (iso- or tertiary)butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and (iso)octyl (meth)acrylate.
As the aromatic group-containing monomer, vinyl monomers having an aromatic group with 6 to 22 carbon atoms are preferred, and styrene monomers, aromatic group-containing (meth)acrylates, and the like are more preferred.
Examples of the styrene-based monomer include styrene, 2-methylstyrene, α-methylstyrene, vinyltoluene, divinylbenzene, etc., and examples of the aromatic group-containing (meth)acrylate include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc. Among these, preferred is one or more selected from styrene, α-methylstyrene, and benzyl (meth)acrylate.

[Nonionic Monomer (a-3)]
The nonionic monomer (a-3) is a monomer having high affinity for water and water-soluble organic solvents. As the nonionic monomer (a-3), polyalkylene glycol (meth)acrylate and alkoxy polyalkylene glycol (meth)acrylate are preferable, and methoxy polyethylene glycol (n=1 to 30) (meth)acrylate is more preferable.
Specific examples of commercially available nonionic monomers (a-3) include the NK Ester M series manufactured by Shin-Nakamura Chemical Co., Ltd., and the Blenmar PE series, PME series, 50PEP series, and 50POEP series manufactured by NOF Corporation.

(Content of each component in raw material monomer (a) or each structural unit in vinyl resin)
The contents of the components (a-1), (a-2), and (a-3) in the raw material monomer (a) during production of the vinyl resin (content as unneutralized amount; the same applies hereinafter) or the contents of the structural units derived from the component (a-1), the structural units derived from the component (a-2), and the structural units derived from the component (a-3) in the vinyl resin are as follows, from the viewpoint of improving the dispersion stability of the pigment.
The content of the (a-1) component is preferably 5 mass% or more, more preferably 10 mass% or more, even more preferably 15 mass% or more, and is preferably 45 mass% or less, more preferably 40 mass% or less, even more preferably 35 mass% or less.
The content of the (a-2) component is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less.
The content of the component (a-3) is 0% by mass or more, and when the component (a-3) is contained, it is preferably 1% by mass or more and preferably 20% by mass or less, more preferably 10% by mass or less.

(Production of vinyl resin)
The vinyl resin can be produced by copolymerizing a monomer mixture containing the raw material monomer (a) by a known solution polymerization method or the like.
Preferred polymerization conditions vary depending on the type of polymerization initiator, monomer, solvent, etc. used, but usually the polymerization temperature is preferably 30° C. or higher, more preferably 50° C. or higher, and preferably 95° C. or lower, more preferably 80° C. or lower. The polymerization time is preferably 1 hour or longer, more preferably 2 hours or longer, and preferably 20 hours or shorter, more preferably 10 hours or shorter. The polymerization atmosphere is preferably a nitrogen gas atmosphere, an inert gas atmosphere such as argon, etc.
From the viewpoint of improving the adsorptivity to the pigment and the dispersion stability, the weight average molecular weight of the vinyl resin is preferably 5,000 or more, more preferably 8,000 or more, and even more preferably 10,000 or more, and is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less.
From the viewpoints of pigment dispersibility and polymer adsorption, the acid value of the vinyl resin is preferably 100 mgKOH/g or more, more preferably 150 mgKOH/g or more, even more preferably 200 mgKOH/g or more, and is preferably 350 mgKOH/g or less, more preferably 300 mgKOH/g or less, even more preferably 270 mgKOH/g or less.
The weight average molecular weight and acid value of the vinyl resin can be measured by the method described in the Examples.

[Preparation of Pigment-Containing Crosslinked Polymer Particles A]
The pigment-containing crosslinked polymer particles A are particles in which the crosslinked polymer a2 is adsorbed to the surface of the pigment, and can stably disperse the pigment in the ink.
From the viewpoint of efficient production, the pigment-containing crosslinked polymer particles A are preferably produced as a pigment aqueous dispersion by a method having the following steps 1 to 3. When no organic solvent is contained in step 1, step 2 (organic solvent removal step) can be omitted.
Step 3 (crosslinking step) is optional. A crosslinking agent may be added in step 1 to form a crosslinked structure on the surface layer of the pigment-containing polymer particles A1 at the same time as coating the pigment with the polymer.
Step 1: A step of dispersing a pigment mixture containing a pigment, a polymer a1, an organic solvent, and water to obtain a dispersion. Step 2: A step of removing the organic solvent from the dispersion obtained in step 1 to obtain an aqueous dispersion of pigment-containing polymer particles A1 (hereinafter also referred to as "pigment aqueous dispersion (i)"). Step 3: A step of adding a crosslinking agent to the pigment aqueous dispersion (i) obtained in step 2 to crosslink the pigment-containing polymer particles A1 to obtain an aqueous dispersion (I) of pigment-containing crosslinked polymer particles A (hereinafter also referred to as "pigment aqueous dispersion (I)").

(Step 1)
The pigment mixture in step 1 is preferably obtained by a method in which polymer a1 is dissolved or dispersed in an organic solvent or water, and then the pigment, water, and, if necessary, a neutralizing agent, a surfactant, etc. are added to the obtained solution and mixed to obtain an oil-in-water dispersion.

When the polymer a1 has acid groups, it is preferable that at least a part of the acid groups is neutralized with a neutralizing agent, which is believed to increase the charge repulsion force exhibited after neutralization, suppress the aggregation of pigment particles in the aqueous ink, suppress thickening, and improve the dispersion stability and storage stability of the pigment.
In the case of neutralization, it is preferable to neutralize the dispersion so that the pH of the dispersion is 7 or more and 11 or less.
Examples of the neutralizing agent include bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, and various amines, with sodium hydroxide and ammonia being preferred, and sodium hydroxide being more preferred.
The neutralizing agent may be used alone or in combination of two or more. The polymer a1 may be neutralized in advance.
From the viewpoint of improving storage stability, the amount of the neutralizing agent used is preferably 10 mol % or more, more preferably 20 mol % or more, even more preferably 30 mol % or more, and is preferably 150 mol % or less, more preferably 120 mol % or less, even more preferably 100 mol % or less.
Here, the equivalent amount of the neutralizing agent used can be calculated by the following formula, where polymer a1 before neutralization is "polymer a1'".
Equivalent amount of neutralizing agent used (mol %)=[{weight (g) of neutralizing agent added/equivalent amount of neutralizing agent}/[{acid value of polymer a1′ (mg KOH/g)×weight (g) of polymer (B)}/(56×1,000)]]×100

In the dispersion treatment in step 1, the pigment particles can be atomized to a desired particle size only by main dispersion using shear stress. However, from the viewpoint of obtaining a uniform aqueous pigment dispersion, it is preferable to pre-disperse the pigment mixture and then further carry out main dispersion.
As a dispersing machine used for preliminary dispersion, a commonly used mixing and stirring device such as an anchor blade or a dispersing blade can be used.
Examples of means for applying the shear stress used in the dispersion include kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersers such as paint shakers and bead mills. Among these, it is preferable to use high-pressure homogenizers and bead mills from the viewpoint of reducing the particle size of the pigment.
When dispersion treatment is performed using a high-pressure homogenizer, the pigment can be controlled to have a desired particle size by controlling the number of passes at a dispersion pressure of 20 MPa or more, and the average particle size of the aqueous pigment dispersion (I) described below can also be adjusted.

(Step 2)
Step 2 is a step of removing the organic solvent from the dispersion obtained in step 1 to obtain a pigment water dispersion (i) of the pigment-containing polymer particles A1. The organic solvent can be removed by a known method. It is preferable that the organic solvent in the obtained pigment water dispersion (i) is substantially removed, but it may remain as long as it does not impair the object of the present invention. The amount of the residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.
In addition, for the purpose of removing coarse particles and the like, it is preferable that the aqueous dispersion from which the organic solvent has been removed is further centrifuged, and then the liquid layer portion is filtered through a filter or the like, and the pigment aqueous dispersion (i) is obtained by passing through the filter or the like.
Examples of commercially available aqueous dispersions of pigment-containing polymer particles A1 include polyacrylic acids such as "Aron AC-10SL" (manufactured by Toagosei Co., Ltd.), and styrene-acrylic resins such as "Joncryl 67", "Joncryl 611", "Joncryl 678", "Joncryl 680", "Joncryl 690" and "Joncryl 819" (all manufactured by BASF Japan Ltd.).

(Step 3)
Step 3 is a step of adding a crosslinking agent to the pigment water dispersion (i) obtained in step 2 to crosslink the pigment-containing polymer particles A1 to obtain a pigment water dispersion (I) of pigment-containing crosslinked polymer particles A.
In step 3, a part of the carboxyl groups of the polymer a1 constituting the pigment-containing polymer particle A1 is crosslinked to form a crosslinked structure in the surface layer of the pigment-containing polymer particle A1. This causes the polymer a2 formed by crosslinking the polymer a1 to be firmly adsorbed or fixed on the pigment surface, suppressing aggregation of the pigment, and as a result, it is believed that the storage stability and substrate adhesion of the resulting ink are further improved.

(Crosslinking Agent)
Preferred examples of the crosslinking agent include a compound having two or more epoxy groups in the molecule, a compound having two or more oxazoline groups in the molecule, and a compound having two or more carbodiimide groups in the molecule.
Specific examples of the compound having an epoxy group include polyglycidyl ethers such as polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether. Among these, preferred are one or more selected from trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, and 1,6-hexanediol diglycidyl ether, and more preferred are trimethylolpropane polyglycidyl ether and 1,6-hexanediol diglycidyl ether.
Examples of commercially available compounds having an oxazoline group include Epocross WS series products and K series products manufactured by Nippon Shokubai Co., Ltd.
Specific examples of compounds having a carbodiimide group include high molecular weight polycarbodiimides produced by decarboxylation condensation reaction of diisocyanate compounds in the presence of a carbodiimide catalyst. Commercially available examples of such products include Carbodilite series products manufactured by Nisshinbo Chemical Inc.

From the viewpoint of improving storage stability, the crosslinking rate of the pigment-containing polymer particles A1 in step 1 or step 3 is preferably 10 mol % or more, more preferably 20 mol % or more, even more preferably 30 mol % or more, and is preferably 80 mol % or less, more preferably 70 mol % or less, even more preferably 60 mol % or less, and still more preferably 50 mol % or less, in terms of the ratio of the molar equivalent number of the crosslinkable functional groups of the crosslinking agent to the molar equivalent number of the carboxy groups of the polymer a1.
From the same viewpoints as above, the temperature of the crosslinking treatment is preferably 40° C. or higher, more preferably 50° C. or higher, even more preferably 60° C. or higher, and preferably 95° C. or lower, more preferably 85° C. or lower, even more preferably 75° C. or lower.
From the viewpoints of completion of the crosslinking reaction and economic efficiency, the time for the crosslinking treatment is preferably 0.5 hours or more, more preferably 1 hour or more, even more preferably 1.5 hours or more, and is preferably 12 hours or less, more preferably 10 hours or less, even more preferably 8 hours or less, and still more preferably 5 hours or less.

The non-volatile component concentration (solid content concentration) of the resulting pigment water dispersion (I) is, from the viewpoint of improving the dispersion stability of the pigment water dispersion and facilitating the production of the ink, preferably 10 mass % or more, more preferably 15 mass % or more, and is preferably 55 mass % or less, more preferably 50 mass % or less.
The solids concentration is measured by the method described in the Examples.
From the viewpoint of dispersion stability, the content of the pigment in the pigment water dispersion (I) is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less.
The mass ratio of the crosslinked polymer a2 constituting the pigment-containing crosslinked polymer particle A in the pigment water dispersion (I) to the pigment [crosslinked polymer a2/pigment] is preferably 8/92 or more, more preferably 10/90 or more, even more preferably 12/88 or more, and is preferably 45/55 or less, more preferably 40/60 or less, even more preferably 35/65 or less.
From the viewpoint of improving storage stability, the average particle size of the pigment-containing crosslinked polymer particles A is preferably 50 nm or more, more preferably 80 nm or more, even more preferably 100 nm or more, and is preferably 400 nm or less, more preferably 350 nm or less, even more preferably 300 nm or less.
The average particle size of the polymer particles is measured by the method described in the Examples.

<Water-insoluble polymer particles B containing no pigment>
From the viewpoint of improving adhesion to a print medium, the ink of the present invention contains water-insoluble polymer particles B that do not contain a pigment (polymer particles B). Polymer particles B are water-insoluble polymer particles that do not contain a pigment and are composed of a water-insoluble polymer b (hereinafter also referred to as "polymer b").
The "water-insoluble" of the polymer b is defined the same as that of the polymer a1.
Examples of the polymer b include condensation polymers such as polyurethane and polyester, and vinyl polymers such as acrylic polymers, styrene polymers, styrene-acrylic polymers, butadiene polymers, styrene-butadiene polymers, vinyl chloride polymers, vinyl acetate polymers, and acrylic silicone polymers. As the polymer particles B, water-insoluble acrylic polymer particles B1 and water-insoluble polyurethane resin particles B2 are more preferable from the viewpoints of accelerating the drying property on the printing medium and improving the adhesion to the substrate.

[Water-insoluble acrylic polymer particles B1]
When the polymer b is an acrylic polymer, the polymer b may be the same as or different from the polymer a1 described above, but preferably contains a structural unit derived from (meth)acrylic acid (b-1) and a structural unit derived from a (meth)acrylic acid ester (b-2).
From the viewpoint of improving the adhesion to the substrate and the storage stability, the (meth)acrylic acid (b-1) is preferably at least one selected from acrylic acid and methacrylic acid, and more preferably methacrylic acid.
From the viewpoint of improving the adhesion to the substrate and the storage stability, the (meth)acrylic acid ester (b-2) is preferably one or more selected from methyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate, more preferably one or more selected from methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate, and more preferably 2-ethylhexyl (meth)acrylate.

The acrylic polymer b may contain structural units derived from monomers other than the above (b-1) and (b-2). Examples of the other monomers include ionic monomers other than (meth)acrylic acid, hydrophobic monomers having aromatic groups, and nonionic monomers, with hydrophobic monomers having aromatic groups being preferred, such as the above-mentioned styrene-based monomers, aromatic group-containing (meth)acrylates, and aromatic group-containing monomer-based macromonomers.

From the viewpoint of improving the adhesion to a substrate and the storage stability, the content of the structural unit derived from (meth)acrylic acid (b-1) in the acrylic polymer b is preferably 1 mass % or more, more preferably 1.5 mass % or more, even more preferably 2 mass % or more, and is preferably 20 mass % or less, more preferably 10 mass % or less, even more preferably 5 mass % or less.
From the viewpoint of improving the adhesion to a substrate and the storage stability, the content of the structural unit derived from the (meth)acrylic acid ester (b-2) in the acrylic polymer b is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and is preferably 99% by mass or less, more preferably 98.5% by mass or less, even more preferably 98% by mass or less.

From the viewpoint of improving the adhesion to the substrate and the storage stability, the weight average molecular weight of the acrylic polymer b is preferably 10,000 or more, more preferably 50,000 or more, and even more preferably 100,000 or more, and is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,200,000 or less.
The glass transition temperature (Tg) of the acrylic polymer b is preferably 0° C. or higher, more preferably 10° C. or higher, even more preferably 20° C. or higher, still more preferably 30° C. or higher, and is preferably 75° C. or lower, more preferably 70° C. or lower, and even more preferably 60° C. or lower.
From the viewpoint of improving the adhesion to the substrate and the storage stability, the average particle size of the water-insoluble polymer particles B1 is preferably 30 nm or more, more preferably 50 nm or more, even more preferably 70 nm or more, and is preferably 180 nm or less, more preferably 150 nm or less, even more preferably 120 nm or less.
The weight average molecular weight of the polymer, the glass transition temperature (Tg), and the average particle size of the polymer particles are measured by the methods described in the Examples.

(Synthesis of Water-Insoluble Acrylic Polymer Particles B1)
The water-insoluble acrylic polymer particles B1 can be produced by copolymerizing a mixture of (meth)acrylic acid and a (meth)acrylic acid ester by a known polymerization method.
In the polymerization, a persulfate such as ammonium persulfate or potassium persulfate, a water-soluble azo polymerization initiator, or the like can be used as a polymerization initiator, and from the viewpoint of improving the dispersion stability of the resin particles, a nonionic surfactant such as polyoxyethylene alkyl ether, polyoxyethylene alkylaryl ether, polyoxyethylene fatty acid ester, or oxyethylene/oxypropylene block copolymer can be used as a surfactant.
The preferable polymerization conditions vary depending on the type of polymerization initiator, but are similar to the polymerization conditions for the vinyl resin in the pigment-containing polymer particles A1.

From the viewpoint of compatibility with aqueous inks, the water-insoluble acrylic polymer particles B1 are preferably used as an aqueous dispersion (emulsion) of polymer particles in which water is the main dispersion medium without removing the solvent used in the polymerization reaction. The polymer particles are preferably neutralized with a neutralizing agent.
Commercially available examples of dispersions of water-insoluble acrylic polymer particles B1 include emulsions of acrylic resins such as "Neocryl A-1127" (manufactured by DSM, anionic self-crosslinking aqueous vinyl resin) and "Joncryl 390" (manufactured by BASF Japan Ltd.), styrene-acrylic resins such as "Joncryl 7100", "Joncryl 7600", "Joncryl 734", "Joncryl 780", "Joncryl 537J", and "Joncryl 538J" (all manufactured by BASF Japan Ltd.), and vinyl chloride-acrylic resins such as "Vinyblan 700" and "Vinyblan 701" (manufactured by Nissin Chemical Industry Co., Ltd.).

[Water-insoluble polyurethane resin particles B2]
The water-insoluble polyurethane resin particles B2 can be obtained by synthesizing polyurethane A by addition reaction of polyol, diisocyanate, and dialkanol carboxylic acid, and then neutralizing the carboxyl groups in polyurethane A with a neutralizing agent and dispersing the polyurethane A in water.
In the above addition reaction, a chain extender or a reaction terminator may be used in combination as necessary. Alternatively, polyurethane A may be reacted in a multi-stage process to synthesize a urethane prepolymer, and then this prepolymer may be mixed with water while being neutralized with a neutralizing agent to carry out a water extension reaction and simultaneously dispersed in water to produce the polyurethane. In this case, viscosity adjustment and solvent distillation are easy, which is preferable from the viewpoint of production. In this way, a particulate polyurethane having an average particle size of 0.01 to 1 μm can be obtained in the form of an emulsion.

The polyol is not particularly limited as long as it is a compound having two or more hydroxyl groups in one molecule, but polyether polyols, polycarbonate polyols, and polyester polyols are preferred, polyether polyols and polycarbonate polyols are more preferred, and polyether polyols are even more preferred.
That is, the water-insoluble polyurethane resin particles B2 are preferably polyether-based polyurethane resin particles or polycarbonate-based polyurethane resin particles, and more preferably polyether-based polyurethane resin particles.

Examples of polyether polyols include polymers obtained by ring-opening polymerization of cyclic ether compounds such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and tetrahydrofuran, either alone or in combination, using a compound having an active hydrogen atom as a catalyst. Specific examples include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.
As the reaction solvent for the polyol and the diisocyanate, from the viewpoint of emulsifying the reaction product, acetone, methyl ethyl ketone, ethyl acetate, etc. are preferred.
Polycarbonate polyols can be obtained by reacting a carbonate compound such as dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, or diethylene carbonate with an aliphatic diol having a carbon chain length of 4 to 9.

Examples of the diisocyanate include chain aliphatic isocyanates such as tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, and trimethylhexamethylene diisocyanate, cyclic aliphatic isocyanates, aromatic isocyanates, and modified products of these diisocyanates. Among these, aliphatic diisocyanates are preferred.
The dialkanol carboxylic acid is a component for introducing an anionic hydrophilic group to stably disperse the polyurethane in water, and examples thereof include dimethylol acetic acid, dimethylol propionic acid, etc. These carboxylic acids can be neutralized with a neutralizing agent to form an aqueous dispersion.
The molecular weight of the reaction product of the polyol and the diisocyanate can be further increased by using a known chain extender such as a polyol or a polyamine, if necessary. As a reaction terminator, a monoalcohol or a monoamine can be used.

It is preferable to use the water-insoluble polyurethane resin particles B2 as an aqueous dispersion in which the water-insoluble polyurethane resin particles B2 are dispersed in water. Examples of commercially available dispersions include "NeoRez R-650" (containing polyether-based polyurethane resin particles) manufactured by DSM, "NeoRez R-9603" (containing polycarbonate-based polyurethane resin particles) manufactured by DSM, and the "WBR" series manufactured by Taisei Fine Chemical Co., Ltd.

[Neutralization of Pigment-Free Water-Insoluble Polymer Particles B]
The water-insoluble polymer particles B (polymer particles B) not containing a pigment are preferably used as an aqueous dispersion as described above, and when obtaining the aqueous dispersion, it is preferable that the polymer b constituting the polymer particles B is neutralized with a neutralizing agent.
Examples of the neutralizing agent include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, ammonia, and organic amine compounds described below, with sodium hydroxide and organic amine compounds described below being preferred, and organic amine compounds described below being more preferred. The neutralizing agents can be used alone or in combination of two or more.

The aqueous ink for plate printing of the present invention contains an organic amine compound described below as a neutralizing agent from the viewpoint of improving the transferability and substrate adhesion of the ink. It is also preferable to use an organic amine compound as a neutralizing agent during the preparation of polymer particles B and to contain the organic amine compound in the aqueous dispersion of polymer particles B.
The equivalent amount (mol %) of the neutralizing agent used is preferably 10 mol % or more, more preferably 30 mol % or more, and preferably 150 mol % or less, more preferably 120 mol % or less, from the viewpoint of the dispersion stability of the polymer particles B. The equivalent amount of the neutralizing agent used can be determined by the same method as described above.
From the viewpoint of dispersion stability, the acid value of the water-insoluble acrylic polymer and the water-insoluble polyurethane is preferably 5 mgKOH/g or more, more preferably 10 mgKOH/g or more, and preferably 50 mgKOH/g or less.

<Organic amine compounds>
The water-based ink for plate printing of the present invention contains an organic amine compound as a neutralizing agent from the viewpoint of improving the transferability and substrate adhesion of the ink.
The organic amine compound is preferably a water-soluble organic amine compound.
"Water-soluble" for an organic amine compound means that the solubility in 100 g of water at 25° C. (hereinafter also simply referred to as "water solubility") is 5 g/100 g _{H 2} O or more. For example, triethylamine has a water solubility of 9 g/100 g _{H 2} O at 25° C., and N,N-dimethylethanolamine (dimethylaminoethanol) has a water solubility of 95.4 g/100 g _{H 2} O at 25° C.

From the viewpoint of improving the transferability of the ink and the adhesion to the substrate in plate printing, the organic amine compound is preferably a water-soluble organic amine compound having a carbon number of preferably 2 or more, more preferably 3 or more, and preferably 8 or less, more preferably 6 or less.
The boiling point of the organic amine compound is preferably 85° C. or higher, more preferably 100° C. or higher, and even more preferably 120° C. or higher, from the viewpoint of improving the transferability of the ink and the adhesion to the substrate in plate printing, and is preferably 250° C. or lower, more preferably 200° C. or lower, and even more preferably 180° C. or lower, from the viewpoint of improving water resistance.
Specific examples of the organic amine compound include water-soluble alkanolamines having 2 to 8 carbon atoms, such as trialkylamines having 3 to 8 carbon atoms, such as triethylamine; primary alkanolamines, such as monoethanolamine, monopropanolamine, and monobutanolamine; secondary alkanolamines, such as N-methylethanolamine, N-ethylethanolamine, N-methylpropanolamine, diethanolamine, and diisopropanolamine; and tertiary alkanolamines, such as N,N-dimethylethanolamine, N,N-dimethylpropanolamine, N,N-diethylethanolamine, N-ethyldiethanolamine, N-methyldiethanolamine, triethanolamine, and triisopropanolamine.

Among the above organic amine compounds, from the viewpoint of improving the transferability of the ink and the adhesion to the substrate in plate printing, preferably there is used one or more selected from trialkylamines having from 3 to 8 carbon atoms, and alkanolamines having from 2 to 8 carbon atoms, more preferably there is used one or more selected from triethylamine (boiling point 89° C.), diethanolamine (boiling point 280° C.), N-methyldiethanolamine (boiling point 247° C.), N,N-dimethylethanolamine (boiling point 135° C.) and triethanolamine (boiling point 335° C.), and even more preferably there is used one or more selected from triethylamine and N,N-dimethylethanolamine.
The organic amine compounds may be used alone or in combination of two or more.
In the present invention, other water-soluble basic compounds may be contained in addition to the organic amine compounds, as long as the effects of the present invention are not impaired. Examples of other water-soluble basic compounds include alkali metal hydroxides such as sodium hydroxide.

<Water-soluble organic solvent>
The water-based ink for plate printing of the present invention contains a water-soluble organic solvent having a boiling point of 100° C. or more and 260° C. or less from the viewpoint of improving the transferability and substrate adhesion of the ink.
The water-soluble organic solvent may be liquid or solid at room temperature (25° C.). The water-soluble organic solvent refers to an organic solvent that dissolves in 100 ml of water at 25° C. in an amount of 10 ml or more.
From the same viewpoints as above, the boiling point of the water-soluble organic solvent is preferably 110° C. or higher, more preferably 115° C. or higher, even more preferably 118° C. or higher, and preferably 250° C. or lower, more preferably 240° C. or lower, even more preferably 235° C. or lower.
Here, the boiling point refers to the standard boiling point (boiling point at 1 atmospheric pressure), and when two or more water-soluble organic solvents are used, the boiling point is a weighted average value weighted by the content (mass%) of each water-soluble organic solvent.

Examples of the water-soluble organic solvent include (i) glycol ethers, (ii) polyhydric alcohols such as propylene glycol, (iii) nitrogen-containing heterocyclic compounds such as N-methyl-2-pyrrolidone and 2-pyrrolidone, and (iv) alkanolamines. Among these, (i) glycol ethers are more preferable.
(i) The glycol ether is preferably one or more selected from alkylene glycol monoalkyl ethers and alkylene glycol dialkyl ethers, and more preferably alkylene glycol monoalkyl ethers. The number of carbon atoms in the alkyl group of the glycol ether is 1 or more, preferably 2 or more, more preferably 3 or more, and preferably 6 or less, more preferably 5 or less, and even more preferably 4 or less. The alkyl group may be linear or branched.

Examples of alkylene glycol monoalkyl ethers include ethylene glycol monoethyl ether (boiling point 136° C.), ethylene glycol monoisopropyl ether (boiling point 142° C.), ethylene glycol monopropyl ether (boiling point 151° C.), ethylene glycol monobutyl ether (boiling point 171° C.), diethylene glycol monomethyl ether (boiling point 194° C.), diethylene glycol monoethyl ether (boiling point 202° C.), diethylene glycol monoisopropyl ether (boiling point 207° C.), diethylene glycol monoisobutyl ether (boiling point 220° C.), diethylene glycol monobutyl ether (boiling point 230° C.), triethylene glycol monomethyl ether (boiling point 248° C.), dipropylene glycol monobutyl ether (boiling point 231° C.), dipropylene glycol monomethyl ether (boiling point 189° C.), and tripropylene glycol monomethyl ether (boiling point 243° C.).
Among these, one or more selected from ethylene glycol monoisopropyl ether, ethylene glycol monopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monoisobutyl ether, and diethylene glycol monobutyl ether are preferred, and one or more selected from ethylene glycol monoisopropyl ether (boiling point 142° C.), diethylene glycol monoisopropyl ether (boiling point 207° C.), and diethylene glycol monoisobutyl ether (boiling point 220° C.) are more preferred.

(ii) The polyhydric alcohol is preferably at least one selected from alkanediols having 2 to 6 carbon atoms, such as propylene glycol (boiling point 188°C), diethylene glycol (boiling point 245°C), and 1,2-hexanediol (boiling point 223°C), and polypropylene glycol having a molecular weight of 500 to 1,000.
In the present invention, an organic solvent other than the water-soluble organic solvent having a boiling point of 100° C. or more and 260° C. or less may be contained within a range that does not impair the effects of the present invention. Examples of the other organic solvent include monohydric alcohols such as ethanol, isopropyl alcohol, and n-propyl alcohol. Examples of water-soluble organic solvents having a boiling point of more than 260° C. include triethylene glycol (boiling point 285° C.), tripropylene glycol (boiling point 273° C.), and glycerin (boiling point 290° C.).

<Surfactant>
The water-based ink for plate printing of the present invention preferably contains a surfactant from the viewpoint of improving the transferability and substrate adhesion of the ink.
As the surfactant, a nonionic surfactant is preferable, and from the viewpoint of improving the transferability and substrate adhesion of the ink, one or more surfactants selected from acetylene glycol-based surfactants and silicone-based surfactants are more preferable, and it is even more preferable to use an acetylene glycol-based surfactant and a silicone-based surfactant in combination.

(Acetylene glycol surfactant)
Examples of acetylene glycol surfactants include acetylene diols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, 2,4-dimethyl-5-hexyne-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, and 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, and ethylene oxide adducts thereof.
The sum (n) of the average number of moles of ethyleneoxy groups (EO) added in the ethylene oxide adduct is preferably 1 or more, more preferably 1.5 or more, and is preferably 20 or less, more preferably 10 or less.
Commercially available examples of acetylene glycol surfactants include the "Surfynol" series and "Olfine" series manufactured by Nissin Chemical Industry Co., Ltd., and the "Acetylenol" series manufactured by Kawaken Fine Chemical Co., Ltd. Among these, preferred are Surfynol 104PG50 (propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active content 50%), Surfynol 420 (EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, n: 1.3), Surfynol 440 (average number of moles of EO added: 3.5), Surfynol 465 (average number of moles of EO added: 10), Olfine E1010, Acetylenol E100, Acetylenol E200, Acetylenol E40, Acetylenol E60, Acetylenol E81, Acetylenol E100, and the like.

(Silicone surfactant)
Examples of silicone surfactants include surfactants such as dimethylpolysiloxane, polyether-modified silicone, amino-modified silicone, and carboxy-modified silicone, and from the same viewpoint as above, polyether-modified silicone surfactants are preferred.
Polyether-modified silicone surfactants have a structure in which the side chain and/or terminal hydrocarbon group of silicone oil is replaced with a polyether group.As the polyether group, polyethyleneoxy group, polypropyleneoxy group, polyalkyleneoxy group in which ethyleneoxy group (EO) and propyleneoxy group (PO) are added in block form or randomly are suitable, and compounds in which polyether group is grafted to silicone main chain, compounds in which silicone and polyether group are bonded in block form, etc. can be used.

From the viewpoint of solubility in ink, the HLB (hydrophilic lipophilic balance) value of the polyether-modified silicone surfactant is preferably at least 2, more preferably at least 3, and even more preferably at least 4. Here, the HLB value can be determined by the Griffin method.
The polyether-modified silicone surfactant preferably has a kinetic viscosity of 50 mm ² /s or more, more preferably 80 mm ² /s or more, and preferably 500 mm ² /s or less, more preferably 300 mm ² /s or less at 25° C. The kinetic viscosity can be determined by an Ubbelohde viscometer.
Commercially available examples of polyether-modified silicone surfactants include the KF series (KF-353, KF-355A, KF-642, KF-6011, etc.) manufactured by Shin-Etsu Chemical Co., Ltd., the Silface SAG series manufactured by Nissin Chemical Industry Co., Ltd., and the BYK series manufactured by BYK Japan K.K.
Among these, the KF series products manufactured by Shin-Etsu Chemical Co., Ltd. are preferred.

[Production of water-based ink for plate printing]
The aqueous ink for plate printing of the present invention can be efficiently produced by mixing the pigment water dispersion (I), the aqueous dispersion of polymer particles B, an organic amine compound, a water-soluble organic solvent having a boiling point of 100° C. or more and 260° C. or less, and, if necessary, a surfactant and further other organic solvents. There is no particular limitation on the method of mixing them. The ink of the present invention may be used as it is after adjusting the content and concentration of each component to the content and concentration at the time of printing, or a previously prepared base ink may be diluted with water or the like and adjusted to the content and concentration at the time of printing.

The content of each component in the water-based ink for plate printing of the present invention and the ink physical properties are as follows. The content of each component in the ink indicates the content at the time of printing.
(Pigment content)
From the viewpoint of print density, the content of the pigment in the ink is preferably 1 mass % or more, more preferably 3 mass % or more, and even more preferably 5 mass % or more, and from the viewpoint of lowering the ink viscosity when the solvent evaporates and improving the storage stability, the content of the pigment in the ink is preferably 15 mass % or less, more preferably 10 mass % or less, and even more preferably 7 mass % or less.
The mass ratio of the pigment to the total solids content of the ink [pigment/(total solids content of ink)] is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, from the viewpoint of improving the transferability of the ink and the adhesion to the substrate in plate printing, and is preferably 0.8 or less, more preferably 0.7 or less, even more preferably 0.6 or less.

(Content of Pigment-Containing Crosslinked Polymer Particles A)
The content of the pigment-containing crosslinked polymer particles A in the ink is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more, from the viewpoint of improving the print density, and is preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of improving the storage stability.
(Content of Polymer Particles B)
From the viewpoint of improving the transferability of the ink and the adhesion to the substrate in plate printing, the content of polymer particles B in the ink is preferably 0.3% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and is preferably 7% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less.

The mass ratio of polymer particles B to pigment-containing crosslinked polymer particles A [polymer particles B/pigment-containing crosslinked polymer particles A] is preferably 0.2 or more, more preferably 0.4 or more, even more preferably 0.6 or more, from the viewpoint of improving the transferability of the ink and the adhesion to the substrate in plate printing, and is preferably 2 or less, more preferably 1.8 or less, even more preferably 1.5 or less.

From the viewpoint of improving the transferability of the ink and the adhesion to the substrate in plate printing, the mass ratio of the polymer to the pigment in the ink [polymer/pigment] is preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.4 or more, and is preferably 3 or less, more preferably 2.5 or less, even more preferably 2 or less.
Since the ink of the present invention contains pigment-containing crosslinked polymer particles A and polymer particles B, the amount of polymer in the above mass ratio [polymer/pigment] is the total amount of crosslinked polymer a2 and polymer b.

The mass ratio of the crosslinked polymer a2 to the polymer b constituting the polymer particles B [crosslinked polymer a2/polymer b] is preferably 0.1 or more, more preferably 0.12 or more, even more preferably 0.14 or more, from the viewpoint of improving the transferability of the ink and the adhesion to the substrate in plate printing, and is preferably 1 or less, more preferably 0.8 or less, even more preferably 0.5 or less.

(Organic amine compound content)
From the viewpoint of improving adhesion to the substrate, the content of the organic amine compound in the ink is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.03% by mass or more, and is preferably 1.5% by mass or less, more preferably 0.8% by mass or less, even more preferably 0.5% by mass or less.
(Content of Water-soluble Organic Solvent)
The content of the water-soluble organic solvent having a boiling point of 100°C or more and 260°C or less in the ink is 1% by mass or more and 30% by mass or less, and from the viewpoint of improving the transferability of the ink and the adhesion to the substrate in plate printing, it is preferably 1.5% by mass or more, more preferably 2% by mass or more, even more preferably 4% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less.
The ink may contain an organic solvent having a boiling point of less than 100°C and more than 260°C. From the viewpoint of improving the transferability and substrate adhesion of the ink in plate printing, the content of such an organic solvent is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

(Surfactant content)
From the viewpoint of improving wettability to the printing medium, the content of the surfactant in the ink is preferably 0.1 mass % or more, more preferably 0.2 mass % or more, even more preferably 0.5 mass % or more, and preferably 5 mass % or less, more preferably 4 mass % or less, even more preferably 3 mass % or less.
From the same viewpoints as above, the content of the acetylene glycol-based surfactant in the ink is preferably 0.2 mass% or more, more preferably 0.4 mass% or more, even more preferably 0.6 mass% or more, and preferably 4 mass% or less, more preferably 3 mass% or less, even more preferably 2 mass% or less.
From the same viewpoints as above, the content of the silicone-based surfactant in the ink is preferably 0.01 mass% or more, more preferably 0.03 mass% or more, even more preferably 0.05 mass% or more, and is preferably 3 mass% or less, more preferably 2 mass% or less, even more preferably 1 mass% or less.

(Water Content)
From the viewpoint of improving the transferability and substrate adhesion of the ink in plate printing, the water content in the ink is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, still more preferably 66% by mass or more, and is preferably 80% by mass or less, more preferably 78% by mass or less, even more preferably 76% by mass or less, and still more preferably 74% by mass or less.
When the ink contains optional components other than the pigment-containing crosslinked polymer particles A, the polymer particles B, the organic amine compound, the water-soluble organic solvent having a boiling point of 100° C. or more and 260° C. or less, the surfactant, and water, a part of the water content can be replaced with the optional components.
The ink of the present invention may contain various additives such as a pH adjuster, a viscosity adjuster, a defoamer, a preservative, and a rust inhibitor as optional components depending on the application.

(Ink properties)
The Zahn cup No. 3 viscosity (Zahn seconds) of the ink at 20° C. is preferably 10 seconds or more, more preferably 12 seconds or more, even more preferably 13 seconds or more, and is preferably 25 seconds or less, more preferably 20 seconds or less, even more preferably 18 seconds or less, from the viewpoint of improving the transferability of the ink in plate printing and the adhesion to the substrate.
The pH of the ink at 20°C is preferably 5.5 or more, more preferably 6.0 or more, and even more preferably 6.5 or more from the viewpoint of improving dispersion stability, and is preferably 11.0 or less, more preferably 10.5 or less, and even more preferably 10.0 or less, from the viewpoints of component resistance and skin irritation.

[Plate printing method]
The plate printing method of the present invention is a method for printing on a low liquid-absorbent printing medium using the water-based ink of the present invention.
Examples of plate printing include gravure printing, flexographic printing, letterpress printing, etc., which use printing plates such as intaglio, lithographic, and letterpress. The water-based ink for plate printing of the present invention has excellent transferability and excellent adhesion to a substrate after transfer, and from the viewpoint of making the most of these features, gravure printing is preferred.
By printing the ink of the present invention on a printing medium by gravure printing, it is possible to obtain a high-definition gravure print having excellent transferability and adhesion to the substrate.
Gravure printing is a method of printing characters and images by supplying the ink to the surface of a rotating gravure cylinder (gravure plate) with concave cells formed on its surface, scraping off the ink with a doctor blade fixed in a predetermined position, leaving the ink only within the cells, and pressing a continuously supplied printing medium against the gravure cylinder with an impression cylinder with a rubber surface, transferring only the ink within the cells of the gravure cylinder to the printing medium.

(Print media)
As the printing medium, a printing medium having low liquid absorption, such as low liquid absorption coated paper or resin film, is preferable.
Examples of coated paper include general-purpose glossy paper and multi-color form glossy paper.
Examples of the resin film include transparent synthetic resin films, such as polyester films, vinyl chloride films, polypropylene films, polyethylene films, nylon films, etc. From the viewpoint of suitability for post-processing such as punching after printing, polyester films and polypropylene films are preferred.
These films may be biaxially stretched films, uniaxially stretched films, or non-stretched films. Among these, polyester films and stretched polypropylene films are more preferred, and from the viewpoint of improving suitability for gravure printing, polyester films such as corona-discharge-treated polyethylene terephthalate (PET) films and stretched polypropylene films such as corona-discharge-treated biaxially stretched polypropylene (OPP) films are more preferred.

In the following manufacturing examples, examples, and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows.

(1) Measurement of the weight average molecular weight of the polymer The weight average molecular weight was measured by gel permeation chromatography (GPC apparatus (HLC-8320GPC) manufactured by Tosoh Corporation, columns (TSKgel Super AWM-H, TSKgel Super AW3000, TSKgel guardcolum Super AW-H) manufactured by Tosoh Corporation, flow rate: 0.5 mL/min) using a solution in which phosphoric acid and lithium bromide were dissolved in N,N-dimethylformamide to concentrations of 60 mmol/L and 50 mmol/L, respectively, as an eluent, and using a monodisperse polystyrene kit with known molecular weights (PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500), manufactured by Tosoh Corporation) as a standard substance.
The measurement sample was prepared by mixing 0.1 g of polymer with 10 mL of the eluent in a glass vial, stirring with a magnetic stirrer at 25° C. for 10 hours, and filtering with a syringe filter (DISMIC-13HP, made of PTFE, 0.2 μm, manufactured by Advantec Co., Ltd.).

(2) Measurement of average particle size of pigment-containing polymer particles A and polymer particles B Cumulant analysis was performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.) to measure the average particle size. A dispersion diluted with water so that the concentration of the particles to be measured was 5 x ^10-3 % by weight (solid content concentration equivalent) was used. The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative times. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent, and the obtained cumulant average particle size was taken as the average particle size of the pigment-containing polymer particles A and polymer particles B.

(3) Measurement of solid content concentration Using an infrared moisture meter "FD-230" (Kett Electric Laboratory Co., Ltd.), 5 g of a measurement sample was dried under conditions of a drying temperature of 150°C and measurement mode 96 (monitoring time 2.5 minutes/fluctuation range 0.05%), and the moisture content (%) of the measurement sample was measured and the solid content concentration was calculated by the following formula.
Solid content (%) = 100 - moisture content (%) of measurement sample

(4) Measurement of acid value of polymer The resin was dissolved in a titration solvent of toluene and acetone (2:1) in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with 0.1 N potassium hydroxide/ethanol solution by potentiometric titration. The inflection point on the titration curve was taken as the end point. The acid value was calculated from the titration amount of the potassium hydroxide solution up to the end point.

(5) Measurement of glass transition temperature (Tg) of water-insoluble polymer Using a differential scanning calorimeter (Q100, manufactured by TA Instruments Japan), the sample was heated to 200° C. and cooled from that temperature at a rate of 10° C./min to 0° C. Next, the sample was heated at a rate of 10° C./min to 200° C. for measurement.
Among the endothermic peaks observed, the temperature of the peak with the largest peak area was determined as the maximum endothermic peak temperature, and this peak temperature was taken as the glass transition temperature (Tg).

(6) Measurement of boiling point of organic solvent: The measurement was carried out according to JIS K2254, and the initial boiling point was regarded as the boiling point.

Production Example 1 (Production of Pigment Water Dispersion A-1)
(1) 236 parts of ion-exchanged water was weighed into a 2 L flask, and 60 parts of a styrene-acrylic polymer (manufactured by BASF, product name: JONCRYL 690, solids concentration 20%, weight average molecular weight: 16500, acid value: 240 mgKOH/g, Tg: 105° C.) and 36.5 parts of a 5N sodium hydroxide solution (sodium neutralization degree 60 mol%) were added. The mixture was stirred for 2 hours at 200 rpm using an anchor blade, and 332.5 parts of an aqueous polymer solution (solids concentration 19.9%) was obtained.
331.7 parts of the aqueous polymer solution and 150.35 parts of ion-exchanged water were placed in a 2 L vessel equipped with a disper blade, and stirred at 1,400 rpm for 15 minutes using a disper (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disper) while cooling in a 0° C. water bath.
(2) Then, 200 parts of magenta pigment (C.I. Pigment Red 146) was added and stirred at 6400 rpm for 1 hour. The dispersion was charged into a wet disperser (Hiroshima Metal & Machinery Co., Ltd., product name: Ultra Apex Mill UAM05) filled with 80% by volume of zirconia beads (Nikkato Co., Ltd., product name: XTZ Ball, 0.3 mmφ), and dispersed five times at a peripheral speed of 8 m/s and a flow rate of 200 g/min while cooling with cooling water at 5°C, and then filtered using a 200 mesh wire net.
(3) To 500 parts of the filtrate obtained in (2) above (150.0 parts of pigment, 45.0 parts of polymer), 9.93 parts of a crosslinking agent (manufactured by Nagase ChemteX Corporation, Denacol EX-321L, trimethylolpropane polyglycidyl ether, epoxy equivalent: 129) (40 mol% equivalent to the carboxylic acid serving as a crosslinking reaction site contained in the acrylic acid in the polymer), 1.2 parts of Proxel LV(S) (manufactured by Lonza Japan Co., Ltd., antifungal agent, active content 20%) were added, and 91.6 parts of ion-exchanged water was further added. The mixture was stirred at 70°C for 3 hours, and then filtered through a 200 mesh wire net to obtain 602.7 parts of an aqueous dispersion A-1 of pigment-containing crosslinked polymer particles (solid content: 34.0%, pigment: 24.9%, polymer: 9.1%, average particle size: 280 nm).

Production Example 2 (Production of Pigment Water Dispersion A-2)
(1) 187.7 parts of the aqueous polymer solution obtained in Production Example 1(1) and 220.9 parts of ion-exchanged water were placed in a 2 L vessel equipped with a disper blade, and the mixture was stirred at 1,400 rpm for 15 minutes using a disper (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disper) while cooling in a water bath at 0° C.
(2) Then, 200 parts of a magenta pigment (C.I. Pigment Red 146) was added, and a filtrate was obtained in the same manner as in Production Example 1(2).
(3) To 500 parts of the filtrate obtained in (2) above (163.8 parts of pigment, 31.2 parts of polymer), 6.88 parts of a crosslinking agent (manufactured by Nagase ChemteX Corporation, Denacol EX-321L, trimethylolpropane polyglycidyl ether, epoxy equivalent 129) (40 mol% equivalent to the carboxylic acid that serves as a crosslinking reaction site contained in the acrylic acid in the polymer), 1.2 parts of Proxel LV (S) (manufactured by Lonza Japan Co., Ltd., antifungal agent, active content 20%) were added, and 85.7 parts of ion-exchanged water was further added. The mixture was stirred at 70°C for 3 hours, and then filtered through a 200 mesh wire net to obtain 593.8 parts of an aqueous dispersion A-2 of pigment-containing crosslinked polymer particles (solid content: 34.0%, pigment: 27.6%, polymer: 6.4%, average particle size: 280 nm).

Production Example 3 (Production of Pigment Dispersion A-3)
(1) 331.3 parts of the aqueous polymer solution obtained in Production Example 1(1) and 238.7 parts of ion-exchanged water were placed in a 2 L vessel equipped with a disper blade, and the mixture was stirred at 1,400 rpm for 15 minutes using a disper (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disper) while cooling in a water bath at 0° C.
(2) Next, 180 parts of a black pigment (C.I. Pigment Black 7), 14.54 parts (40 mol % equivalent to the carboxylic acid serving as a crosslinking reaction site contained in the acrylic acid in the polymer, manufactured by Nagase ChemteX Corporation, Denacol EX-321L, trimethylolpropane polyglycidyl ether, epoxy equivalent: 129), and 1.53 parts of Proxel LV(S) (manufactured by Lonza Japan Ltd., antifungal agent, active content 20%) were added and stirred at 6,400 rpm for 1 hour.
(3) The obtained dispersion was charged into a wet disperser (manufactured by Hiroshima Metal & Machinery Co., Ltd., product name: Ultra Apex Mill UAM05) filled with 80% by volume of zirconia beads (manufactured by Nikkato Corporation, product name: XTZ Ball, 0.3 mmφ), and dispersed for 5 passes at a peripheral speed of 8 m/s and a flow rate of 200 g/min while cooling with cooling water at 15° C., and then filtered using a 200 mesh wire screen to obtain 766.1 parts of aqueous dispersion A-3 of pigment-containing crosslinked polymer particles (solid content concentration: 34.0%, pigment: 23.5%, polymer: 10.5%, average particle size: 220 nm).

Production Example 4 (Production of Pigment Dispersion A-4)
(1) 331.3 parts of the aqueous polymer solution obtained in Production Example 1(1) and 54.7 parts of ion-exchanged water were placed in a 2 L vessel equipped with a disper blade, and the mixture was stirred at 1,400 rpm for 15 minutes using a disper (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disper) while cooling in a water bath at 0° C.
(2) Next, 180 parts of a black pigment (C.I. Pigment Black 7), 16.91 parts (corresponding to 40 mol % relative to the carboxylic acid serving as a crosslinking reaction site contained in the acrylic acid in the polymer) (manufactured by Nagase ChemteX Corporation, Denacol EX-212, 1,6-hexanediol diglycidyl ether, manufactured by Nagase ChemteX Corporation, epoxy equivalent: 150) and 0.82 parts of Proxel LV(S) (manufactured by Lonza Japan Ltd., antifungal agent, active content 20%) were added and stirred at 6,400 rpm for 1 hour.
(3) The obtained dispersion was dispersed and filtered in the same manner as in Production Example 3(3) to obtain 583.7 parts of aqueous dispersion A-4 of pigment-containing crosslinked polymer particles (solid content: 45.0%, pigment: 30.8%, polymer: 14.2%, average particle size: 200 nm).

Production Example 5 (Production of Pigment Dispersion A-5)
(1) 226.1 parts of the aqueous polymer solution obtained in Production Example 1(1) and 155.1 parts of ion-exchanged water were placed in a 2 L vessel equipped with a disper blade, and the mixture was stirred at 1,400 rpm for 15 minutes using a disper (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disper) while cooling in a water bath at 0° C.
(2) Next, 180 parts of a magenta pigment (C.I. Pigment Red 146), 82.71 parts (corresponding to 40 mol % relative to the carboxylic acid serving as a crosslinking reaction site contained in the acrylic acid in the polymer) of a crosslinker (manufactured by Nisshinbo Chemical Inc., carbodiimide crosslinking agent, Carbodilite SV-02, NCN equivalent (chemical formula amount per mole of carbodiimide group): 430, solid content: 40%), and 0.82 parts of Proxel LV(S) (manufactured by Lonza Japan Ltd., antifungal agent, active content 20%) were added and stirred at 6,400 rpm for 1 hour.
(3) The obtained dispersion was dispersed and filtered in the same manner as in Production Example 3(3) to obtain 644.7 parts of aqueous dispersion A-5 of pigment-containing crosslinked polymer particles (solid content: 40.0%, pigment: 27.9%, polymer: 12.1%, average particle size: 230 nm).

Production Example 6 (Production of Pigment Dispersion A-6)
(1) 226.1 parts of the aqueous polymer solution obtained in Production Example 1(1) and 153.0 parts of ion-exchanged water were placed in a 2 L vessel equipped with a disper blade, and the mixture was stirred at 1,400 rpm for 15 minutes using a disper (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disper) while cooling in a water bath at 0° C.
(2) Next, 180 parts of a black pigment (C.I. Pigment Black 7), 82.26 parts of a crosslinking agent (manufactured by Nippon Shokubai Co., Ltd., oxazoline-based crosslinking agent, EPOCROS WS-500, oxazoline group amount: 4.5 (mmol/g, solid), solid content: 39%) (corresponding to 40 mol% with respect to the carboxylic acid serving as a crosslinking reaction site contained in the acrylic acid in the polymer), and 0.82 parts of Proxel LV(S) (manufactured by Lonza Japan KK, antifungal agent, active content 20%) were added and stirred at 6,400 rpm for 1 hour.
(3) The obtained dispersion was dispersed and filtered in the same manner as in Production Example 3(3) to obtain 642.2 parts of aqueous dispersion A-6 of pigment-containing crosslinked polymer particles (solid content: 40.0%, pigment: 28.0%, polymer: 12.0%, average particle size: 280 nm).

Production Example 7 (Production of Pigment Water Dispersion A-7)
(1) 331.7 parts of the aqueous polymer solution obtained in Production Example 1(1) and 150.35 parts of ion-exchanged water were placed in a 2 L vessel equipped with a disper blade, and the mixture was stirred at 1,400 rpm for 15 minutes using a disper (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disper) while cooling in a water bath at 0° C.
(2) Then, 200 parts of a magenta pigment (C.I. Pigment Red 146) was added, and a filtrate was obtained in the same manner as in Production Example 1(2).
(3) To 500 parts of the filtrate obtained in (2) above (150.0 parts of pigment, 45.0 parts of polymer), 1.1 parts of Proxel LV(S) (manufactured by Lonza Japan K.K., antifungal agent, active content 20%) was added, and 72.4 parts of ion-exchanged water was further added. The mixture was stirred at 70° C. for 3 hours, and then filtered through a 200 mesh wire screen to obtain 573.5 parts of aqueous dispersion A-7 of pigment-containing polymer particles (solid content: 34.0%, pigment: 26.2%, polymer: 7.8%, average particle size: 280 nm).

Production Example 8 (Production of Water Dispersion of Pigment-Free Water-Insoluble Polymer Particles B1)
Into a reaction vessel equipped with a dropping funnel, 0.5 parts of methacrylic acid, 14.5 parts of methyl methacrylate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 5.0 parts of 2-ethylhexyl acrylate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), LATEMUL E-118B (11.1 parts of sodium polyoxyethylene alkyl ether sulfate, manufactured by Kao Corporation, surfactant), 0.2 parts of potassium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, and 282.8 parts of ion-exchanged water were placed and mixed at 150 rpm, followed by nitrogen gas replacement to obtain an initial charge monomer solution.
A monomer solution containing 9.5 parts of methacrylic acid, 275.5 parts of methyl methacrylate, 95.0 parts of 2-ethylhexyl acrylate, 35.1 parts of LATEMURU E-118B, 0.6 parts of potassium persulfate, and 183.0 parts of ion-exchanged water at 150 rpm was placed in a dropping funnel and replaced with nitrogen gas.
Under a nitrogen atmosphere, the initial monomer solution in the reaction vessel was heated from room temperature to 80° C. over 30 minutes while stirring at 150 rpm, and the monomer in the dropping funnel was gradually dropped into the reaction vessel over 3 hours while maintaining the temperature at 80° C. After the dropping was completed, the mixture was stirred for 1 hour while maintaining the temperature in the reaction vessel, and 204.7 parts of ion-exchanged water was added. Then, the mixture was filtered through a stainless steel wire mesh (200 mesh) to obtain an aqueous dispersion of water-insoluble polymer particles B1 (solid concentration: 40%, average particle size: 100 nm).
The polymer b1 constituting the polymer particles B1 had an acid value of 16 mgKOH/g and a Tg of 48°C.

<Preparation of Water-Based Ink for Gravure Printing>
Example 1 (Preparation of Water-Based Ink 1)
To obtain the ink composition shown in Table 1, 38.18 parts of the pigment water dispersion A-1 obtained in Production Example 1 (corresponding to a pigment concentration of 9.5% in the ink) and 26.25 parts of an emulsion containing polyether-based polyurethane resin particles (manufactured by DSM, product name: NeoRez R-650, containing 38.1% active ingredient and 1.0% triethylamine) were added to a container and stirred at 150 rpm.
Further, 7 parts of diethylene glycol monoisobutyl ether, 0.5 parts of a silicone surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KF-6011, PEG-11 methyl ether dimethicone, kinetic viscosity at 25°C: ¹³⁰ mm2/s, HLB: 12), 2.0 parts of an acetylene glycol surfactant (manufactured by Nissin Chemical Industry Co., Ltd., product name: Surfynol 104PG50, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active content 50%, propylene glycol solution), 1.1 parts of a thickener (manufactured by ADEKA Corporation, product name: ADEKA NOL UH-420, active content 30% aqueous solution), and 24.7 parts of ion-exchanged water were added and stirred at room temperature for 30 minutes, and then filtered through a stainless steel wire mesh (200 mesh) to obtain water-based ink 1.
The composition of the water-based ink 1 is shown in Table 1. The amount of each component in Table 1 is an effective amount.

Examples 2 to 12 and Comparative Examples 1 to 4 (Preparation of Water-Based Inks 2 to 12 and 13 to 16)
Water-based inks 2 to 12 and 13 to 16 were obtained in the same manner as in Example 1, except that the ink compositions in Example 1 were changed as shown in Table 1.

The details of the amounts of each component in Table 1 are as follows.
(Water-soluble organic solvent)
iBDG: diethylene glycol monoisobutyl ether (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., boiling point 220°C)
iPG: Ethylene glycol monoisopropyl ether (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., boiling point 142°C)
IPA: Isopropyl alcohol (manufactured by Fujifilm Wako Pure Chemical Industries, boiling point 83°C)
BTG: Triethylene glycol monobutyl ether (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., boiling point 271°C)
(Neutralizer)
TEA: Triethylamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
DMAE: Dimethylaminoethanol (N,N-dimethylethanolamine, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
NaOH: Sodium hydroxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.)

The water-based inks obtained in the Examples and Comparative Examples were used to carry out the following gravure printing and were evaluated. The results are shown in Table 1.
<Printing test>
Using the inks of the examples and comparative examples, printing was carried out on the corona discharge treated surface of a PET film (manufactured by Futamura Chemical Co., Ltd., FE2001#12, lamination grade).
The printing was performed using a tabletop gravure printing test machine (K Printing Proofer, manufactured by Matsuo Sangyo Co., Ltd.) and a laser-made gravure 250 line, 8 μm plate (manufactured by Nabe Process Co., Ltd.) to perform gradation printing. The obtained print was subsequently dried for 10 minutes in a dryer (Drying Oven DSV402, manufactured by Yamato Scientific Co., Ltd.) set at 60° C.

<Evaluation of transferability>
A 10% halftone dot portion of the obtained print was cut out to 10 mm x 10 mm, magnified with a Peak Loupe 10x manufactured by Tokai Sangyo Co., Ltd., and the number of dots that were not transferred and were missing was counted, and the transferability was evaluated according to the following evaluation criteria.
If the evaluation result is B or higher, the transferability is practically satisfactory.
(Evaluation criteria)
A: Less than 5 B: 5 to less than 10 C: 10 or more

<Evaluation of Adhesion to Substrate>
A cellophane tape (manufactured by Nichiban Co., Ltd., 12 mm width) was applied to the 100% dotted area (solid area) of the obtained print, and after rubbing it firmly with a finger to ensure adhesion, the tape was peeled off to check the state of ink peeling, and the adhesion to the substrate was evaluated according to the following evaluation criteria.
If the evaluation result is B or higher, the adhesion to the substrate is practically satisfactory.
(Evaluation criteria)
A: No peeling B: Less than 20% peeling C: More than 20% peeling

From Table 1, it can be seen that the water-based inks of the Examples have superior ink transferability and substrate adhesion in plate printing compared to the water-based inks of the Comparative Examples.

The water-based ink for plate printing of the present invention has excellent ink transferability and substrate adhesion even to low-absorbency printing media, and can therefore be suitably used for plate printing, particularly gravure printing.

Claims (11)

The ink contains crosslinked water-insoluble polymer particles A containing a pigment, water-insoluble polymer particles B not containing a pigment, an organic amine compound, 1.5% by mass to 15 % by mass of a water-soluble organic solvent having a boiling point of 100° C. or more and 260° C. or less under 1 atmospheric pressure, and water,
the organic amine compound is a trialkylamine having 3 to 8 carbon atoms,
A water-based ink for plate printing, in which the mass ratio of water-insoluble polymer particles B containing no pigment to crosslinked water-insoluble polymer particles A containing a pigment [water-insoluble polymer particles B containing no pigment/crosslinked water-insoluble polymer particles A containing a pigment] is 0.4 or more and 2 or less. The water-based ink for plate printing according to claim 1, wherein the organic amine compound is triethylamine. The water-based ink for plate printing according to claim 1 or 2, wherein the water-soluble organic solvent is a glycol ether. The water-based ink for plate printing according to claim 3, wherein the glycol ether is at least one selected from alkylene glycol monoalkyl ethers and alkylene glycol dialkyl ethers. The aqueous ink for plate printing according to claim 4, wherein the alkylene glycol monoalkyl ether is at least one selected from ethylene glycol monoisopropyl ether, ethylene glycol monopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monoisobutyl ether, and diethylene glycol monobutyl ether. The water-based ink for plate printing according to any one of claims 1 to 5, further comprising a surfactant. The aqueous ink for plate printing according to claim 6, wherein the surfactant contains at least one selected from an acetylene glycol surfactant and a silicone surfactant. The water-based ink for plate printing according to any one of claims 1 to 7, wherein the crosslinked water-insoluble polymer particles A containing a pigment are formed by crosslinking polymer particles A1 containing a pigment with a polyfunctional epoxy compound. The water-based ink for plate printing according to claim 8, wherein the crosslinking rate of the pigment-containing polymer particles A1 is 10 mol % or more and 80 mol % or less. The water-based ink for plate printing according to any one of claims 1 to 9, which is for gravure printing. A plate printing method in which the water-based ink according to any one of claims 1 to 9 is used to print on a low-absorbency printing medium.